1. Field of the Invention
The present invention relates to a positive photoresist composition. Specifically, it relates to a positive photoresist composition that is suitable for the formation of very fine and dense hole patterns comprising very fine holes and having a duty ratio of less than or equal to 1. The duty ratio is expressed by [space (an interval between a hole and another)/hole diameter] and when it is less than or equal to 1, it means that the space is less than or equal to 1 when the hole diameter is defined as 1.
2. Description of the Related Art
Conventional positive photoresist compositions comprising alkali-soluble resins and quinonediazido-group-containing compounds exhibit excellent definition, sensitivity and etching resistance in photolithographic techniques using i-line (365 nm) and have practically been used in the manufacture of semiconductor devices and liquid crystal devices. However, these positive photoresist compositions cannot form satisfactory hole patterns.
With an increasing density of integrated circuits (ICs), the size and interval of patterns become finer and denser, and demands have been made on techniques to form ultrafine patterns each having a hole diameter of less than or equal to half a micron and a duty ratio of less than or equal to 1 in the formation of hole patterns.
However, when the conventional compositions are used for the formation of such ultrafine hole patterns comprising patterns very close to each other, they fail to form separated patterns due to bridge of patterns in many cases.
In addition, even if separated patterns are obtained, the resulting holes do not have satisfactorily vertical profile and have “tapered shapes” in which the diameter of the top of the holes is larger than that of the bottom thereof to thereby cause etching failure and interconnection failure. There have been demands on compositions that can form patterns having improved shapes.
Japanese Patent Application Laid-Open No. 11-15151 (reference 1) discloses a positive photoresist composition for the formation of contact holes, comprising an alkali-soluble resin and a specific naphthoquinonediazido-group-containing compound. The composition can effectively avoid dimple formation in the formation of holes using a halftone mask.
Japanese Patent Application Laid-Open No. 10-69077 (reference 2) discloses a positive photoresist composition comprising 100 parts by weight of an alkali-soluble novolak resin and 0.5 to 10 parts by weight of a specific dissolution accelerator (sensitizer) having phenolic hydroxyl groups. The alkali-soluble novolak resin has a weight average molecular weight (Mw) of 1000 to 10000 and includes 1,2-naphthoquinonediazidosulfonyl groups substituting for 2% to 27% by mole of total hydroxyl groups. The composition can exhibit high definition in the formation of line and space (L & S).
Japanese Patent Application Laid-Open No. 10-97066 (reference 3) discloses a positive photoresist composition comprising a novolak resin and a specific dissolution accelerator (sensitizer) having phenolic hydroxyl groups. The novolak resin has a weight average molecular weight (Mw) of 1000 to 10000 and includes 1,2-naphthoquinonediazidosulfonyl groups substituting for 2% to 27% by mole of total hydroxyl groups. The composition can form “microgrooves”, i.e., resist patterns having constricted bottoms, and is suitable as a material for lift-off technique. These conventional positive photoresist compositions, however, exhibit insufficiently high definition in the formation of hole patterns having a duty ratio of less than or equal to 1.